Comparison of fault tree and integral models for the estimation of nuclear power plant blackout frequency

Fault tree is a well-established analytical technique commonly used in reliability studies. A fault tree model combines the events leading to failure of the system using Boolean logic. For specific analysis like station blackout frequency estimation as a function of blackout duration detailed estimates seems preferable. In this paper, fault tree model is compared with the integral model for the estimation of station blackout frequencies for 1/2 and 1/3 DG configurations. Integral model uses mathematical integration of possible combination of failure events for the frequency estimation. Though integral model is more accurate, the computation becomes complex for higher DG configurations. The results of the two approaches are compared and we arrive at effective value of mission time to be used in fault tree analysis for accurate results consistent with integral model. (author)